Superstrong Nanoillumination Created Inside Metallic Structure

Michael A. Greenwood

Unusually strong nanoillumination has been achieved by researchers using a three-step enhancement process that successively augments light until it reaches intensity levels more than 1000 times stronger than the initial incident light.

This image shows the intensity distribution inside the slit with the nanohole at the bottom. Used with permission of Applied Physics Letters.

Cheng Liu and two other researchers in the department of bioengineering at the National University of Singapore said that their findings could have applications for photonics, super-resolution imaging, optical data storage, nonlinear optics, lithography and other technological areas that require nanoillumination.

The researchers combined a subwavelength slit and a nanohole together into a metallic screen. Incident light with a wavelength of 800 nm was contracted and squeezed through the 40-nm-wide slit on the subwavelength metallic structure with the aid of generated surface plasmon and focused by the self-imaging effect inside the slit. At this point, the technique had increased the intensity of the light by ∼350 times.

To further increase the strength of the light, the team sealed the output end of the slit and focused the light onto a nanohole measuring 80 × 160 nm² situated at the bottom of the slit. The intensity was augmented a second time by the transmission resonance when the light passed through the tiny aperture.

The scientists plan to conduct additional experiments to see whether even higher light intensities can be achieved. They believe that intensities 10 times greater can be attained by corrugating the illumination surface with nanoditches parallel to the slit. The working distance of the light also can be prolonged by fabricating nanograting circling around the exit end of the hole to direct the light.

Applied Physics Letters, Vol. 90, 011501.